This thesis presents the results on data terminal interface and data switching for an experimental PBX system for voice and data switching. First, the structure of the integrated voice/data PBX system is described and the characteristics of the various switching subsystems are discussed. Then, the basic requirement and procedure for data switching and signaling are presented. The data terminal interface, i.e., data circuit terminating equipment has been designed and implemented for various data rates. Finally, its performance has been evaluated.